Most industry analysts expected Windows 8 would go on sale in the fall to ensure that the machines running on the operating system would be available for the holiday shopping season. Consumers and businesses who don’t want to buy new computers will be able to buy Windows 8 and upgrade their systems.

New versions of Windows typically come out every three years, but this update is the most widely anticipated overhaul of the software since 1995.

Applications will appear in a mosaic of tiles on Windows 8. Microsoft also designed the operating system so it can run on personal computers or touch-based tablet computers.